The present invention relates to an image erasing apparatus for erasing an image formed on an image carrier such as a photosensitive drum used in a copying machine.
Conventional image erasing apparatuses used in copying machines can be categorized into two types, i.e., one having an erasing array as shown in FIG. 1, and one having an erasing array as shown in FIG. 2. These apparatuses are disclosed in Japanese Patent Disclosure (Kokai) Nos. 61-177474, 61-177475, 61-177476, and 62-47667.
Erasing array unit 2 shown in FIG. 1 has main printed board 4 on which are mounted ICs (integrated circuits), resistors, capacitors, and the like (all of which are not shown). Auxiliary printed board 8 is connected to main printed board 4 via connecting wiring 6, and has a plurality of light-emitting elements such as light-emitting diode (LED) chips 10 directly bonded to a surface thereof. In addition, the surface of auxiliary printed board 8 is covered with casing 12 such that LED chips 10 are independently covered thereby. Casing 12 is fixed to main printed board 4, and has window holes 14 formed therein which respectively correspond to LED chips 10. Each window hole 14 serves to guide light emitted from its respective LED chip 10 toward a predetermined part of photosensitive drum 16. Transparent dustproof film 18 is adhered to a surface of casing 12, to prevent dust from entering thereinto through window hole 14. Lens 20 is interposed between film 18 and LED chips 10.
Erasing array unit 22 shown in FIG. 2 has main printed board 24 on which are mounted ICs (integrated circuits), resistors, capacitors, and the like (all of which are not shown). Auxiliary printed board 28 is connected to main printed board 24 via connecting wiring 26, and has a plurality of light-emitting elements such as discrete type (lamp bulb type) LEDs 30 are directly bonded to a surface thereof. LEDs 30 is designed such that lens 34 is integrally formed on LED chip 32. In addition, the surface of auxiliary printed board 28 is covered with casing 36 such that LEDs 30 are independently covered thereby. Casing 36 is fixed to main printed board 24, and has windows 38 formed therein which respectively correspond to LEDs 30. Each window 38 serves to guide light emitted from its respective LED 30 toward a predetermined part of photosensitive drum 40. Transparent dustproof film 42 is adhered to a surface of casing 36, to prevent dust from entering thereinto unit through window 38.
In erasing array unit 2 shown in FIG. 1, since lens 20 is arranged between LED chips 10 and film 18, distance L between LED chips 10 and photosensitive drum 16 is increased by the thickness of lens 20. As a result, illuminance on photosensitive drum 16 is decreased. Component parts and assembly steps are increased in number, resulting in an increase in cost. Furthermore, since the optical axes of lens 20 and LED chips 10 tend to deviate from each other, when light emitted from ON LED chip 10 propagates through corresponding lens 20 while being refracted, part thereof is guided to lens 20 corresponding to adjacent OFF LED chip 10, thereby resulting in a stray light phenomenon. Thus, an image formed outside a designated erase range is erased.
In erasing array 22 shown in FIG. 2, since discrete type LED 30 having lens 34 integrally formed on LED chip 32 is used, a distance between LED chip 32 and photosensitive drum 40 is increased by the height of LEDs 30. As a result, illuminance on photosensitive drum 40 is decreased. Furthermore, since it is difficult to mount LEDs 30 on auxiliary printed board 28 with high precision, accurate positioning of LED 30 with respect to window 38 of casing 36 cannot be easily achieved. Therefore, an image within a predetermined erase range cannot be erased with high precision.